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The effects of cold atmospheric-pressure plasma jet (CAPPJ) were investigated on germination and early seedling growth of fenugreek (Trigonella foenum-graecum L) seeds. A two-electrode argon CAPPJ system with and without an additional grounded electrode [accelerating grounded (AG) electrode] was used at different exposure times. After 16 h of observation, the germination rates increased by 4 and 7 times, without and with using an AG electrode, respectively, for 1 min of plasma exposure. An increase in shoot fresh weight was observed, especially at 10 min exposure time. A high dry weight of root and shoot at 1 min-AG exposure time was observed. The root:shoot ratio was lower in plasma-treated seedlings, compared with the control plants. The study found that the O-radical emission line (777.4 nm) enhanced 5 times, due to the presence of an AG electrode, which increased the axial electric field and led to the formation of more streamers. The three stated effects (O-radicals, enhancement of the electric field and streamers) could be the cause for the stimulation of seed germination and seedling growth parameters when using the CAPPJ. The scanning electron microscope images showed the etching of the seed surface layers, which was more pronounced when an AG electrode was applied. The results of the current study indicate that the germination rates increased due to the increase of O-radical concentration and the etching of the seed surfaces.

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Simple argon atmospheric pressure cold plasma jet has been designed and characterized. The spectral and electrical characteristics of the generated plasma jet were investigated. The effects of applied voltage and flow rate on plasma jet length were studied. A sinusoidal high voltage waveform was applied to ignite the plasma jet. Two current pulses were generated per each half cycle of the positive applied voltage while one current pulse was generated in the negative halves of the voltage waveforms. The time interval between the two positive current pulses decreased with increasing the applied voltage. The emission spectra of the plasma specified that the plasma included active species of O• and OH•. In addition, the estimated gas temperature of the generated plasma jet was in the range of 330 K, which nominated this jet to be used to treat heat sensitive materials. The obtained results showed that the length of the plasma jet increased by increasing any of the applied voltage or the flow rate at low values, whereas the length approached steady-state values at higher applied voltages and transient from laminar to turbulent flow mode at higher flow rates. This work is highly useful for applications of the required exposure to active species, charged ions, and UV photons at low operating temperatures and applied voltages.